Fair enough.
I don't recommend going straight to ranked as soon as you're level 30, make sure you're actually good at the game.
I know a couple of people that did ranked as soon as they were 30.
Guess what ? Bronze V, Bronze IV and Bronze V. Yeah.

If you are in a league for 2000 games, you belong there.
I'd say even 200 is enough. If you don't advance after hundrets of games, you are in the league where you belong, end of story. There's a reason pros never end up in "Bronze III Elo Hell" because of bad teammates.

Dude, I strongly recommend not to main teemo. I know he's cool and ****, but he is not the kind of champ you'll use to carry games. And in solo queue you will need that. Check the tier lists and win rates of all champs and pick one of those that suits you best.

Meh, you never know.
Personally, I would love to play just as one champion to climb up, if I were actually bothered to do ranked, and if I weren't as impulsive.
I just decide the champion I'll play whenever I am picking, unless I'm given choices.

Just don't forget some of the rules of ranked in LoL.
Don't be a faggot, don't play the blame game, don't insult your allies.
Do ward, and be friendly. Just a couple, but quite important; You insulting your teammates will usually make them do worse, as they are most probably just pubescent teenagers, so their reactions can be quite bad.